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Powering mobile phones with food waste

Andrew pouring food waste into the blender, which is strong enough to crush chicken bones

Using food waste to power up mobile phones and tablets? This is not science fiction but reality brought about by NUS researchers who have developed a self-sustaining anaerobic biodigester which can digest food waste to produce electrical and heat energy.

The research team is led by Associate Professor Tong Yen Wah from NUS Chemical and Biomolecular Engineering. Assoc Prof Tong is also the Co-Programme Director of the Energy and Environmental Sustainability Solutions for Megacities programme, a research collaboration between NUS and Shanghai Jiao Tong University funded by the National Research Foundation under its Campus for Research Excellence and Technological Enterprise framework.

According to the National Environment Agency, food waste accounts for some 10 per cent of the total waste generated in Singapore, with only 14 per cent of such food waste getting recycled. The volume of food waste in Singapore has increased over the past 10 years and the figure is expected to rise due to the increase in population and economic activity.

NUS researchers designed a self-sustaining biodigester that can use food waste to produce electrical and heat energy

Assoc Prof Tong, who is a Principal Investigator at NUS Environmental Research Institute (NERI), said that the team wanted to help reduce waste in the country. NERI Research Fellow Dr Zhang Jingxin, who designed the self-sustaining anaerobic biodigester, said that it works like a biochemical stomach which breaks down organic matter in an environment without oxygen. “Using a specially formulated mix of anaerobic microorganisms, the digester system efficiently breaks down food waste into biogas that is subsequently converted into heat and electrical energy,” he explained.

Elaborating on the features of the biodigester, Assoc Prof Tong said, “Our digester system is easy to operate, and we can now generate electricity, heat and fertilisers from food waste that would otherwise be disposed of. All the processes in the system can be easily controlled and monitored to ensure optimal performance and safety. For instance, we have sensors that are programmed to send out end-of-process updates and flag any safety concerns in real-time directly to the team via mobile phone alerts.” As part of the process, moisture and trace gases such as hydrogen sulphide — which has a pungent odour — are removed.

The biodigester is self-sustaining, with every component of the system maintained using the electricity and heat produced. The heat output is used to create hot water that is fed back to the jacket encasing the anaerobic biogas tank to keep it at an optimal working temperature of 50 degrees Celsius. Parts such as the control computer, lights, engines, fans and pumps are powered by the electricity generated. Excess electricity is stored in batteries that can be used to charge mobile phones and tablets.

Our digester system is easy to operate, and we can now generate electricity, heat and fertilisers from food waste that would otherwise be disposed of. All the processes in the system can be easily controlled and monitored to ensure optimal performance and safety.

The researchers calculate that a single tonne of food waste can produce about 200 kilowatt-hours to 400 kilowatt-hours of electricity, depending on the composition of the food waste. Food with a higher concentration of carbohydrates, proteins and fats will generate more biogas, yielding more electrical energy. In addition, the system is able to transform about 80 per cent of the food waste fed into it into nutrient-rich digestate, which can be processed to become liquid fertilisers for agricultural and horticultural purposes.

A mobile anaerobic biodigester, housed in a 20-foot container, has been placed at Raffles Hall from late January and targets to treat up to 200kg of food waste daily. The unit takes up two car lots and can be shifted to sites where food waste recycling is required. The excess electrical energy generated is stored in four batteries, which are placed in a mobile phone and tablet charging station situated at the Raffles Hall canteen for complimentary use by students. Assuming typical usage, the four batteries are able to last about three days, said Dr Zhang.

A second stationary unit that is able to handle a larger volume of food waste — up to 400kg — is in the works.

Year 4 NUS Chemical Engineering student Gu Danning, who worked on the system as part of her final year project, demonstrating the phone and tablet charging mechanism

Year 3 Chemical Engineering student Andrew Lee, who worked on the biodigester as part of his undergraduate research project, said that he chose to work on this project as it was related to sustainability, a topic close to his heart. Speaking of the benefits of the system, he said, “I feel that it is a brilliant idea. Everyone is so reliant on their phones nowadays and having the locker installed is also a good way to allow the user to feel secure.” Andrew added that in future, there could be other ways of utilising the energy obtained from food waste, such as powering dining hall lights at night.

The team hopes to expand the project into local residential areas and possibly China as well.